Waste heat is often created as a byproduct of industrial processes where flowing streams of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes utilize heat exchanger devices to capture and recycle waste heat back into the process via other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.
Waste heat can be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic cycles are typically steam-based processes that recover and utilize waste heat to generate steam for driving an expander, such as a turbine, connected to an electric generator, a pump, and/or another device. As an alternative to steam-based, thermodynamic cycles, an organic Rankine cycle utilizes a lower boiling-point working fluid, instead of water. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbon, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa).
A synchronous power generator is a commonly employed turbine generator utilized for generating electrical energy in large scales (e.g., megawatt scale) throughout the world for both commercial and non-commercial use. The synchronous power generator generally supplies electricity to an electrical bus or grid (e.g., an alternating current bus) that usually has a varying load or demand over time. In order to be properly connected, the frequency of the synchronous power generator must be tuned and maintained to match the frequency of the electrical bus or grid. Severe damage may occur to the synchronous power generator as well as the electrical bus or grid should the frequency of the synchronous power generator become unsynchronized with the frequency of the electrical bus or grid.
Turbine generator systems also may suffer an overspeed condition during the generation of electricity—generally—due to high electrical demands during peak usage times. Turbine generator systems may be damaged due to an increasing rotational speed of the moving parts, such as turbines, generators, and/or gears, as well as a deficit in lubricating and cooling such turbomachinery. In addition, the turbines and pumps utilized in turbine generator systems are susceptible to fail due to thermal shock when exposed to substantial and imminent temperature differentials. Such rapid change of temperature generally occurs when the turbine or pump is exposed to a supercritical working fluid. The thermal shock may cause valves, blades, and other parts to crack and result in catastrophic damage to the unit.
The control of the turbine driven pump, such as a turbopump, is quite relevant to the operation and efficiency of an advanced Rankine cycle process. Generally, the control of the turbopump is often not precise enough to achieve the most efficient or maximum operating conditions without damaging the turbopump. Also, during operations, the turbopump generally requires proper lubrication and temperature regulation—often provided by a bearing or seal gas. The turbopump and/or turbomachinery components of the turbopump have very close tolerances and may be susceptible to immediate damage if there is an interruption of the bearing seal gas. If too much or not enough pressure is applied to a thrust bearing of the turbopump, then the rotor of the turbopump is likely to rub against stationary parts, such that the turbopump damages itself and ceases to operate.
Therefore, there is a need for a heat engine system, a turbopump system, and methods for generating mechanical and electrical energy, whereby pressures, temperatures, and lubrication within the turbomachinery is controlled at acceptable levels while maintaining or increasing the efficiency for operating the heat engine system.